(a) Field of the Invention
The present invention relates to a multi-user detection method for canceling MAI (multiple access interference) caused by usage of a plurality of users in a CDMA (code division multiple access) communication system. More specifically, the present invention relates to a method for configuring a multi-user detector using a hybrid interference cancellation method, and canceling the interference using a clustering method that adopts an optimization method for effective interference cancellation, and a realization thereof.
(b) Description of the Related Art
Spread spectrum CDMA methods, such as IS-95 and IMT-2000, have been used as important multiple access methods in second and third generation mobile communications.
Since direct sequence CDMA among them allows a plurality of users to share time and frequencies, the users are determined using signature share time and frequencies, the users are determined using signature sequences.
However, since complete orthogonality between user signature sequences are not guaranteed, cross-correlation exists between the signature sequences, and the corresponding MAI accordingly restricts transmission capacity and performance of the communication systems. The near-far problem also exists, being generated because of differences of users' signal power.
To solve the above-noted problems, multi-user detection methods for canceling the MAI have been proposed.
An optimal detector following the multi-user detection methods has theoretically been found, but since the methods have a calculation complexity level that is an exponential function of the number of users, they are not appropriate for actual realization. Therefore, studies on quasi-optimal detectors with less calculation complexity and allowing some performance deterioration have been undertaken.
With these quasi-optimal detectors, since the interference canceller differs from the linear detector in that it requires no inverse matrix calculation on the cross-correlation matrix, the interference canceller is easier to realize than the linear detector. The realization method includes the SIC (successive interference cancellation) method and the PIC (parallel interference cancellation) method, depending on the configuration.
The SIC method for arranging the signal powers of all users according to their size, sequentially estimating the signals to regenerate them, and canceling them from received signals, provides excellent BERs (bit error rates), but processing delay time increases in proportion to the number of users.
The PIC method concurrently estimates signals of all users in the earlier step to cancel regenerated signals of users other than the corresponding users from the received signals. This PIC method provides a short processing delay time, but problematically increases calculation complexity since the method uses a multi-stage configuration for better performance.
Also, the PIC device outperforms the SIC device when the power control for solving the fundamental problems is complete, and the SIC device outperforms the PIC device when the power control is not complete.
The Korean Application No. 10-2001-13752, “Multi-user interference cancellation apparatus and method” by LG Electronics, discloses a technique related to the interference cancellation. In this application, by arranging all the multi-user signal powers in descending sequence to cancel the interference, a multi-user interference canceller and a method thereof with somewhat increased calculation but better performance is provided. However, the interference cancellation method increases the processing delay time in proportion to the number of users.